EDYTA DZIEMINSKA

Overall efficiency of internal combustion engines are heavily depended on intake air temperature which is directly related to the heat transfer inside an intake system. Previously, authors developed an equation by using port model setup to calculate Nusselt number with introduction of Graetz and Strouhal numbers. This study modified the port model equation to improve its accuracy in a real engine experimental setup. Predicted intake air temperature was compared to the measured data with a maximum error of 5.6%. Additionally, 100 K of temperature difference was found between the boost pressure values of 944hPa and 678hPa from 1-D engine simulation results.

To investigate the safety properties of high-pressure hydrogen discharge or leakage, an under-expanded hydrogen jet flow with a storage pressure of 82 MPa from a small jet orifice with a diameter of 0.2 mm is studied by three-dimensional (3D) numerical calculations. The full 3D compressible Navier-Stokes equations are utilized in a domain with a size of about 3 × 3 × 6 m which is discretized by employing an adaptive mesh refinement (AMR) technology to reduce the number of grid cells. By AMR, the local mesh resolutions can narrowly cover the Taylor microscale lT and direct numerical simulations (DNS) are performed. Both the instantaneous and mean hydrogen concentration distributions in the present jet are discussed. The instantaneous concentrations of hydrogen CH2 on the axis presents significant turbulent pulsating oscillations. The centerline value of the intensity of concentration fluctuation σˆH2 asymptotically comes to 0.23, which is in a good agreement with the existing experimental results. It substantiates the conclusion that the asymptotic centerline value of σˆH2 is independent of jet density ratio. The probability distributions function (PDF) of instantaneous axial CH2 agree approximately with the Gaussian distribution while skewing a little to the higher range. The time averaged hydrogen concentration C¯H2 along the radial directions can also be described as a Gaussian distribution. The axial C¯H2 of 82 MPa hydrogen jet tends to obey the distribution discipline approximated with C¯H2 =4200/(z/θ) where z is the axial distance from the nozzle and θ is the effective ejection diameter, which is consistent with the experimental results. In addition, the hydrogen tip penetration Ztip is found to be in a linear relationship with the square root of jet flow time t. Meanwhile, the jet's velocity half-width LVh approximately gains an linear relation with z which can be expressed as LVh=0.09z.

Detonation in ducts is usually studied assuming adiabatic walls because of the high kinetic energy due to the incoming flow being supersonic. In the present work, numerical simulations of deflagration-to-detonation transition (DDT) using a detailed chemical reaction model are performed under adiabatic and isothermal boundary conditions in a tube with no-slip walls. The results show a local explosion driving DDT, which occurs near the tube wall in the case of an adiabatic wall, but close to the flame front in the case of an isothermal wall. Furthermore, to examine the effects of a turbulent boundary layer, a simulation using the Baldwin-Lomax turbulence model is carried out. In the case of the isothermal wall, there is again a local explosion near the tube wall, which leads to detonation. In summary, the present study confirms that the boundary conditions affect the transition to detonation and that the boundary layer is a key component of DDT.

Experiments concerning a fast flame have been performed by many researchers, but it is impossible to observe some phenomena in the experimental frames only. The aim of this study is to show the numerical analysis of the fast flame that leads to deflagration-to-detonation transition (DDT). It was found that flame propagates with a supersonic velocity for some time before it transits to detonation. Additionally a new flame is developed in the vicinity of the wall due to compression shocks heating up the mixture along with adiabatic wall conditions. Moreover, on the tip of each flame one can observe a dense high-pressure and high-temperature region that forms a small but strong bow shock. This shock may be partly a clue in flame acceleration and DDT.

In this study Lewis number (Le) for laminar premixed flame in oxy-hydrogen stoichiometric mixture was investigated numerically. This is the first time to analyze values of Le for the whole flow field. It is known from definition that low Le is beneficial in flame propagation and our numerical simulations are a proof for that. On the edge of the flame Le is extremely low, which indicates that the flame accelerates. Flame can propagate with more than a speed of sound in the reactive mixture, which results in deflagration-to-detonation transition (DDT) and detonation. The present paper shows such propagating process with low Le as well as the profiles of Le in the DDT domain.